Danish version of the National Institutes of Health-Chronic Prostatitis Symptom Index (NIH-CPSI) questionnaire: a linguistic translation, cross-cultural adaptation and test-re-test reliability study.

To translate and cross-culturally adapt the National Institutes of Health-Chronic Prostatitis Symptom Index (NIH-CPSI) into Danish and assess the reliability of the translated version. The NIH-CPSI was translated into Danish by a formalized translation procedure. Study participants suffering from Chronic Prostatitis/Chronic Pelvic Pain Syndrome (CP/CPPS) were recruited from a CP/CPPS newsletter email-list. The translated questionnaire was tested for face validity by interviewing men ( = 7) suffering from CP/CPPS. Relative reliability (interclass correlations coefficient, ICC) and absolute reliability (minimal detectable change, MDC; and standard error of measurement, SEM) were assessed on an electronic version of the Danish NIH-CPSI, including a general response assessment of symptom stability at the second assessment. One hundred and twenty-nine men volunteered for the test-re-test study, 43 did not fit the eligibility criteria or had incomplete tests and 27 were excluded due to symptom changes between test and re-test, leaving 59 participants for the reliability study. The relative reliability for the total NIH-CPSI score was found to be an excellent ICC of 0.93 (95% CI = 0.91-0.96). The absolute reliability for the total NIH-CPSI score revealed an MDC of 5.0 and a SEM of 1.8, corresponding to 12% and 4%, respectively, of the maximal obtainable NIH-CPSI score. The NIH-CPSI questionnaire was successfully translated and cross-culturally adapted into a Danish version. An electronic version of the Danish NIH-CPSI showed excellent reliability. The questionnaire is suitable for use as an outcome measure in research studies and may also be a useful tool in the clinical setting.